The present invention relates to per se novel pyridine-3-peroxycarboxylic acid monopersulfate having the formula (I): ##STR2## and concerns, mereover, the process for the preparation thereof and the use thereof as bleaching agent.
The pyridine-3-peroxycarboxylic acid monopersulfate having the above defined formula (I) represents a product having a high interest from an industrial viewpoint, with particular reference to the high content of active oxygen per weight unit.
In an more specific way, for example, the pyridine-3-peroxycarboxylic acid monopersulfate having the above defined formula (I) finds a particularly efficacious application in the field of bleaching, in the industry of detergence.
Under this point of view, in the last years, the organic peroxyacids aroused an increasing interest in the industrial field, particularly due to their excellent possibilities for use as bleaching agents in formulations for medium low temperature washing, even more widespread due also to energy-saving considerations.
Therefore, the research activity is aimed at finding organic peroxyacid compounds endowed with the necessary requisites of bleaching activity, thermal stability and storage stabilityor shelf life.
Therefore, many either mono- or di-peroxycarboxylic, straight or cyclic, organic peroxyacids are known and used, among others, in the detergent field.
Already described peroxycarboxylic acids are, e.g.: diperoxydodecanedioic acid, monoperoxyphthalic acid, diperoxyazelaic acid and substituted diperoxyglutaric and adipic acids, etc.
Applicants are not aware of pyridine-3-peroxycarboxylic acid monopersulfate having the above-reported formula (I) nor of any process for its preparation.
The conventional percarboxylation process of hydrogen contemplates carrying out the oxidation of the substrate with a solution of hydrogen peroxide, in concentrated H.sub.2 SO.sub.4.
The strong acidity of the reaction medium and the presence in the substrate, used as starting material, of a salifiable nitrogen atom of basic character confers to the said substrate a high solubility in the acidic medium, making it impossible to apply any of the conventional processes for the isolation of the peroxycarboxylic acid derivative which may be formed such as by precipitation by dilution with water or by extraction with an organic solvent which is selective for the peroxycarboxylic acid product and is not miscible in the remaining reaction mixture.
Surprisingly, it has been discovered by the Applicants that the pyridine-3-peroxycarboxylic acid monopersulfate having the formula (I), salified on the nitrogen atom with the persulfuric acid, subject matter of the present invention, may be obtained by means of a novel process which is also a part of the present invention.
One object of the present invention is to provide, as per se novel compound, the pyridine-3-peroxycarboxylic acid monopersulfate having the above formula (I).
Another object is to provide a simple and cheap process for the preparation of the above peroxycarboxylic acid monopersulfate having the above formula (I).
A further object is the use of the 3-pyridine-peroxycarboxylic acid monopersulfate having the above formula (I) as bleaching agent in detergent formulations; and especially those destined for low-medium temperature use.
These, and still other objects which will become even clearer for those skilled in the art from the following detailed disclosure, are achieved, according to the present invention, by the 3-pyridine-peroxycarboxylic acid monopersulfate having the above formula (I), and by the relevant preparation process, characterized in that nicotinic acid or pyridine-3-carboxylic acid or its N-sulfate salt is reacted with H.sub.2 O.sub.2 in concentrated H.sub.2 SO.sub.4, and in that the peroxycarboxylic acid monopersulfate (I) is then separated from the reaction mixture by the addition of ethyl acetate.
In this way the peroxycarboxylic acid monopersulfate having the formula (I) is obtained, as a crystalline solid, by means of their insolubilization in the reaction medium by the ethyl acetate solvent.
Described in a somewhat explicit way, the process according to the present invention consists in the peroxycarboxylation reaction of the pyridine-3-carboxylic acid or of its N-sulfate salt, in an acid medium of concentrated H.sub.2 SO.sub.4, with H.sub.2 O.sub.2 and in the subsequent addition, at the end of the reaction, of ethyl acetate.
This involves the consequent separation of the pyridine-3-peroxycarboxylic acid monopersulfate product having the formula (I), in a stable solid form.
As said above, the pyridine-3-carboxylic acid substrate used as the starting material may be, optionally, already salified as sulfate on the Nitrogen atom.
The substrate used as the starting material is a compound per se known (nicotinic acid).
The obtained product is then filtered, washed with the solvent, dried and so forth, according to per se known techniques.
According to a preferred operating mode, the reaction of peroxycarboxylation of the pyridine-3-carboxylic acid, used as the starting substrate, or of its N-sulfate, is carried out by gradually adding H.sub.2 O.sub.2, having a concentration within the range of from approximately 70% to approximately 90% by weight, to a solution of the substrate in concentrated H.sub.2 SO.sub.4 (96-98%), by maintaining the reaction temperature throughout the reaction course within the range of 0.degree. and 25.degree. C.
Otherwise, it has been found to be operatively possible to prepare in advance the salt of the substrate, in the form of N-sulfate, by processing under the same conditions as shown above, but in the absence of H.sub.2 O.sub.2, and by separating the thus-obtained salt which is then peroxidized.
The amount of H.sub.2 SO.sub.4 determined at a concentration of 100%, is substantially equal to 9 moles per mole of substrate.
The hydrogen peroxide is used in an amount which is in excess with respect to the substrate, substantially equal to 5.5 moles per mole of substrate.
The amount of ethyl acetate used is at least equal to 4 liters/substrate mole and furthermore, it is added at a temperature not higher than approximately 40.degree. C.
The pyridine-3-peroxycarboxylic acid monopersulfate product having formula (I) is usually solid at room temperature. It may be especially useful in formulations of detergent compositions, e.g., granular formulations, as bleaching agents in solution over a wide temperature range.
The detergent compositions may be formulated according to the usual pertinent techniques, together with other components and/or additives, etc.
The present invention is now disclosed in still further detail in the following examples, which are supplied for purely illustrative and not limiting purposes.
The pyridine-3-peroxycarboxylic acid monopersulfate was characterized by elemental analysis, by determining its content of active oxygen (by iodometric titration), and by using Fourier Transform Infrared Spectroscopy (FT-IR).